Antenna arrays with elements aperiodically arranged to reduce grating lobes



Aug. 11, 1970 v o. F. BOWMAN 3,524,133

ANTENNA ARRAYS WITH ELEMENTS APERIODICALLY v ARRANGED TO REDUCE GRATING LOBES Filed Aug. 24, 1967 3 Sheets-Sheet 2 fgm 19 Bra/41 murmur/ml .W/Hik nut 147m 9 ww- FAM/ Fiifl J. ole/v5? -rmsu:4u mwkaz I IVVE N T 00 94w; 550M114 ATTUIIEY Aug. 11, 1970 o. F. BOWMAN 3,524,188

ANTENNA ARRAYS WITH ELEMENTS APERIODICALLY ARRANGED TO REDUCE GRATING LOBES Filed Aug. 24, 1967 5 Sheeis-Sheef 3 INVENTOR ATTORNEY United States Patent US. Cl. 343-754 9 Claims ABSTRACT OF THE DISCLOSURE A transfer array antenna made up of a primary array, a secondary array, and a plurality of transmission lines coupled therebetween to form a transfer array is described in this disclosure. The primary array is made up of a plurality of antenna modules with each antenna module being further divided into orthogonal dipole elements. Likewise, the secondary array is made up of a plurality of antenna modules which are further divided into orthogonal dipole elements. A separate pair of transmission lines is coupled between each one of the antenna modules of the primary array and a corresponding antenna module of the secondary planar array. The transmission lines include phase shifters which, when appropriately phased, control the beam of the array antenna. The antenna is fed by means of a feed horn which directs the RF signal energy toward and receives the RF signal energy from the primary array.

BACKGROUND OF INVENTION Periodic arrangement of antenna modules to form an overall grid array antenna is known in the state of the art. The term antenna modules refers to the separate antenna blocks or subdivisions which when combined together form the overall grid array. The antenna modules may be a single radiating element such as a pyramidal horn or may be modules made up of a plurality of radiating elements. The number of antenna modules used for a given level of required performance may easily run into several thousands. A first restriction on the minimal number of antenna modules is imposed by the scan angle and scan loss requirements. A second restriction on the minimal number of antenna modules is imposed by the requirement for a given level of performance with respect to secondary lobes. The second restriction may be more limiting than the first when the array antenna used is required only to scan a limited range. One reason for the large number of modules required for a given level of performance is often due to the fact that the array factor attains a value of unity in one or more directions other than that at the peak of the main beam, thereby creating grating side lobes.

Transfer antenna arrays of the type comprising a primary array subdivided into a grid of antenna modules, a secondary array subdivided into a grid of antenna modules and transmission paths coupled between each primary antenna module and its corresponding secondary antenna module are known in the state of the art. These transfer arrays because of the grating side lobes require a large number of antenna modules for a given level of performance. The requirement for a large number of antenna modules both adds to the cost of the antenna array and makes the antenna array impractical for many uses.

It is an object of this invention to provide an improved array antenna in which a minimum number of antenna modules are required for a given level of array performance.

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It is a'further object of this invention to provide an improved circular grid array antenna.

It is still a further object of this invention to provide an improved multiple-polarized transfer array antenna.

BRIEF DESCRIPTION OF INVENTION Briefly these and other objects of the present invention are provided in one embodiment by arranging a plurality of substantially identical antenna modules in a grid configuration so as to fill an antenna array aperture. RF signal energy is fed over separate transmission paths to each of the antenna modules. A separate phase shifter is coupled to each of the separate transmission paths to control the phase of each antenna module to provide beam scanning. The antenna modules are arranged in an aperiodic manner so that the array factor attains a value of unity for a given level of performance only at the peak of the main beam, thus eliminating grating side lobes while permitting a reduction in the number of modules required for a given level of performance.

DESCRIPTION OF THE INVENTION The applicants invention will be further described with reference to the following accompanying drawing, in which FIG. 1 is a cut-away view of a transfer array in accordance with one embodiment of the present invention;

FIG. 2 is a perspective sketch of one primary antenna module;

FIG. 3 is a partial sketch of the secondary array;

FIG. 4 is a sketch of a circular grid secondary array consisting of concentric rings of secondary antenna modules in accordance with an embodiment of this invention;

FIG. 5 is a diagram of a transmission path through a. cell of a transfer array antenna in accordance with an embodiment of the present invention; and

FIG. 6 is a sketch of a spiral grid array in accordance with another embodiment of this invention.

FIG. 1 shows a cut-away View of a transfer array antenna 10. The transfer array antenna 10 is constructed basically of a primary array 11, a secondary array 12 and a pair of transmission paths 13, 14 between the primary array 11 and the secondary array 12. The primary array 11 is shown as a spherical section adapted to receive spherical wave RF energy from a feed horn 15. The primary array 11 is subdivided into a grid of identical antenna modules 16. FIG. 2 illustrates one primary antenna module 16 having a pair of orthogonally positioned dipoles 20 and 21 mounted to a rectangular reflector sheet 22. The dipoles 20 and 21 are coupled through the refiector sheet 22 to separate input-output ports 23 and 24 on the opposite side of the primary antenna module 16. The dipole elements 20 and 21 are positioned on the spherical surface of the array 11 facing the feed horn so as to coupled the spherical wave RF energy to the separate ports 23, 24. Each pair of dipoles 29 and 21 for each primary antenna module 16 is arranged in identical orientation relative to the respective antenna module 16. In this case one dipole 2!} of each antenna module 16 is positioned parallel to one side 17 of the antenna module 16 and the other dipole 21 of each antenna module 16 is positioned parallel to the adjacent side 18. The feed horn 15 is positioned and arranged with respect to the primary array 11 so as to properly feed the spherical wave RF energy to the dipole elements and 21 of the spherical primary array 11. Conventional feed systems, not shown, couple the RF signal energy to and from the feed horn 15.

The secondary array 12 is subdivided to form a planar grid of identically shaped or nearly identically shaped secondary antenna modules 19. FIG. 4 is a partial sketch of the secondary array 12 showing some of the secondary antenna modules 19. Although FIG. 4 shows only some of the secondary antenna modules, it is to be understood that the entire surface of the array 12 is filled therewith. As shown in FIG. 3, each secondary antenna module 19 in this embodiment is made up of identical circuit assemblies of dipoles 26, 27 mounted to the rectangular reflector sheets 28. The plurality of dipoles 26 in one orientation are placed with the plane of polarization orthogonal to the plane of polarization of the other plurality of dipoles 27 to form orthogonal dipole pairs. The dipoles 26, 27 are oriented parallel to the adjacent sides of the secondary antenna module 19. Each secondary antenna module 19 is identical or nearly identical to that shown in FIG. 3 and all dipoles 26, 27 of each secondary antenna module are similarly oriented with respect to the adjacent side of each respective secondary antenna module 19. The plurality of dipoles 26 in one orientation in each secondary antenna module 19 are coupled to one port 30 shown as a dot on the back of the secondary antenna modules 19 in FIG. 1. The plurality of dipoles 27 in the opposite orthogonal polarization are coupled to a separate port 31 also shown as a dot on the back of the secondary antenna modules 19 in FIG. 1.

The secondary antenna modules 19 that make up the secondary planar array 12 are arranged in a planar circular grid configuration as shown in FIG. 4. The secondary antenna modules 19 are arranged in concentric rings 25 in a manner so as to fill the antenna array as completely as possible and thereby provide the most efiicient use of the grid antenna area. In such an arrangement slight variations in the shape and size of the secondary antenna modules 19 so as to completely fill the overal array aperture 12 will allow the most efiicient use of the given antenna area. The aperiodic or randomized nature of an elliptical or in this case a circular grid arrangement reduces the number of antenna modules required for a given maximum level of grating lo'bes. This reduction in the number of antenna modules required is due to the fact that for a given level of performance the array factor in a substantially elliptical grid arrangement does not attain a value of unity in any direction other than that of the peak of the main beam. The circular grid arrangement has a certain degree of regularity which permits the use of identical shaped (or nearly identically shaped) antenna modules making the circular grid concept economical to use over certain other array configurations. The substantially elliptical and in this case the circular grid concept is also more economical than other configurations in that due to the aperiodic nature the overall antenna array uses fewer antenna modules, as much as 96 percent reduction, and consequently fewer phase shifters and control circuits for a given level of performance. The primary antenna modules 16 are arranged over the spherical section 11 using a type of circular grid arrangement similar to that employed on the secondary planar array.

A pair of transmission lines 13, 14 are coupled between each primary antenna module 16 and the corresponding secondary antenna module 19. One transmission line 13 of each pair couples one of the dipoles 21 of the antenna module 16 to a plurality of dipoles 27 arranged in the similar orientation of plane of polarization in the corre- SpOnding secondary antenna module 19 through ports 24 and 31. Likewise the other transmission line 14 couples the other orthogonal dipole of the primary antenna module to a plurality of dipoles 26 in similar orientation of plane of polarization in the corresponding secondary antenna module 19 through ports 23 and 30. Each of the transmission lines 13 and 14 are arranged so as to include phase shifters 35, 36 to provide beam control in response to control signals supplied by conventional means not shown. The transmission lines 13 and 14 are all of equal length. The transmission lines 13 and 14 near the center of the transfer antenna 10 has loops 40 and 41 so as to fit between the primary array 11 and secondary array 12.

The use of the circular grid arrangement shown in FIG.

1 requires that each of the primary antenna modules 16 in the spherical primary array 11 be capable of receiving all the RF energy of a wave from the feed 15 incident on its surface independent of the orientation of that primary antenna module 16. This requirement is satisfied by arranging the dipoles 20 and 21 employed in each primary antenna module 16 so as to be capable of receiving two orthogonal linear polarizations. If the polarization of the signal at the feedhorn 15 is to be preserved, the same requirement of orthogonally positioning the dipoles is true of the dipoles elements 26, 27 employed in each secondary antenna module 19. The transfer array 10 re-establishes at all portions of the planar secondary array surface 12 the same state of polarization as that of the wave from the feedhorn 15 at the surface of primary array 11. This is accomplished by coupling like oriented dipoles of the secondary antenna modules to the similarly oriented dipoles of the primary antenna module. Any transmission through the transfer array 10 can be described by tracing the transmission of a linearly polarized wave from the feed through a typical cell consisting of a primary antenna module 16, a secondary antenna module 19 and the twin transmission paths 13, 14.

FIG. 5 shows a diagram of the transmission path through a single cell of the transfer array. Because each of the antenna modules 16 and 19 have identical dipole placement and each are oriented parallel to the adjacent sides of each of the antenna modules, the respective dipoles appear in approximately the same radial and tangential directions when these antenna modules are placed in the circular grid configuration. FIG. 3 shows a typical secondary antenna module 19 made up of radial dipoles 26 and tangential dipales 27 orthogonal to the radial dipoles. The spherical feed wave from the feedhom 15 impinging on the dipole side of the primary array 11 is power divided by the primary antenna modules 16 and transformed into output guided waves at the two primary antenna module 16 output ports 23, 24. For example a horizontally polarized wave from the feed 15 is divided at the primary antenna module 16 into two paths. The amplitude of the waves at the two ports is proportional to the cos and sin 4 where is the angle between the plane of polarization of the feed wave and that of the dipoles. For the horizontally polarized case with the dipoles in radial and tangential orientation the magnitudes of these components are proportional to the cos 3 and sin 4: for the radial and tangential components respectively where is the angular location of the antenna module with respect to the horizontal plane. See FIG. 3. The guided waves propagate to the two ports 30, 31 of the secondary antenna module 19 undergoing identical amounts of phase shift through phase shifters 35, 36. The guided waves are transformed by the secondary antenna modules 19 into a single wave in space that is plane polarized at an angle with respect to the polarization of the secondary dipoles associated with one port. Since the primary and secondary dipoles of any one cell have the same attitude angle with respect to some reference axis in their respective antenna module, the waves from all the secondary dipoles are linearly polarized in the same direction. For the horizontal polarization case illustrated, the secondary antenna module 19 by radiating the radial and tangential components re-establishes the original horizontal polarization. A vertically polarized wave from the feed is similarly processed.

In summary, the primary antenna module resolves the incoming linearly polarized wave from the feed into two component guided Waves which are transferred to the secondary antenna module where the secondary antenna module combines the components into a radiated wave, the plane of polarization of which is equal in angle to that of the feed wave. In an alternative design the dipole elements need not be positioned parallel to the adjacent sides of the antenna module as shown but may each be rotated by the same angle such as 45 degrees in the same direction from the two adjacent sides of the antenna module. It is necessary that the secondary and primary antenna modules be alike with respect to polarization if the polarization is to be re-established. Because of any two orthogonally polarized waves are handled simultaneously and independently by the system, the transfer as described above can handle any complex polarizations established by the feed. Although the operation as described re-establishes the same polarization as at the feed, other variations of the multiple-polarization technique may be used to give a fixed but different rela tionship between polarization of the feed and polarization of the secondary wave radiation. While dipole elements are used in the described embodiment as radiating elements, any type of known state of the art radiating elements such as a pyramidal horn may be used without departing from the scope of this invention.

WVhile the particular embodiment described above shows a circular secondary array configuration, many other substantially elliptical configurations may be used to provide the aperiodic arrangement without departing from the scope of this invention. The circular grid and other elliptical grid configurations provide a certain degree of regularity which permits the use of identically shaped (or nearly identically shaped) antenna modules. The substantially elliptical grid concept is also advantageous since it employs fewer antenna modules and requires fewer phase shifters and control. The equal element antenna module concept is most economical in terms of replacing and constructing the antenna modules.

An alternative circular grid concept having similar properties is one in which the size of the antenna modules increases with the radial distance from the center of the antenna array so that, for example, in connection with a rotationally symmetric radially tapered aperture distribution, a more nearly equal power distribution per antenna module illumination is achieved. Consequently, the power level at each antenna module is lower than that in the equal area antenna module case having the same number L of antenna modules. The equal power element case has applications for high power uses wherein the specific transmission components, for example, phase shifters may otherwise undesirably limit the power handling capability of the antenna. The equal power element case is also of interest in solid state circuit applications wherein each antenna module is furnished with its own solid state transmitter/receiver circuit so that it is desirable to operate these at nearly equal power levels.

The circular grid arrangement requires that an integral number of antenna modules fit well into each annulus or ring. Another elliptical grid con-figuration to reduce the grating side lobes may be provided by a spiral grid arrangement. In the spiral grid one turn corresponds to an annulus and the number of antenna modules in this turn may be non-integral. To fill the area of a circular aperture 50 as shown in FIG. 6 with identical antenna modules 51 each having a dimension d in the radial direction (of the circular aperture), one begins at the outer edge of the antenna aperture 50 and places the antenna modules 51 adjacent to one another along the arm of a contracting spiral which is centered on the antenna aperture and which has a pitch in the radial direction approximately equal to d. The antenna modules shown are square but they may be rectangular, trapezoidal, sectorial, or of other shapes to provide the optimum filling of the aperture 50 for the results desired. In the central region of the aperture it may be desirable to depart from the strict adherence to the spiral grid and to fill this region using an irregular arrangement of antenna modules of standard size or of special shape.

The antenna systems have been described in terms of a transmitting antenna. Because of the reciprosity theory of antennas, the antenna systems function equally well as receiving antennas and the disclosure is not to be considered as limited only to transmit or receive applications.

While certain specific apparatus has been described, it is to be understood that this description is made only by way of example and not as a limitation to the scope of the invention as set forth in the objects and in the accompanying claims.

What is claimed is:

1. An antenna array comprising,

a plurality of substantially identically shaped antenna modules aperiodically arranged in a grid-like fashion across the width of the aperture of the array so as to fill the aperture of said antenna array,

means for feeding RF electromagnetic signal energy over separate transmission paths to each of said antenna modules,

means coupled to each of said separate transmission paths to control the phase of each of said antenna modules to provide control of the main 'beam of said array.

2. The combination as claimed in claim 1 wherein said antenna modules are arranged in a circular grid configuration.

3. The combination as claimed in claim 1 wherein said antenna modules are arranged in a spiral grid configuration.

4. The combination as claimed in claim 1 wherein said feed means includes a second array having an equal number of antenna modules similarly arranged in an aperiodic manner across the width of the second array aperture and responsive to said RF signal energy to distribute the RF energy over said separate transmission paths coupled between each first mentioned antenna module and a corresponding antenna module of said second array.

5. A transfer array antenna comprising:

a primary array including a plurality of primary antenna modules aperiodically arranged in a grid-like fashion across the width of the primary array aperture so as to fill the aperture of the primary array with each primary antenna module having at least one pair of orthogonally positioned radiating elements oriented in a given manner with respect to the sides of said primary antenna module,

a secondary array including a plurality of secondary antenna modules aperiodically arranged across the width of the secondary array aperture in grid-like fashion so as to fill the aperture of the secondary array with each secondary antenna module having at least one pair of orthogonally placed radiating elements oriented in said given manner with respect to the sides of said secondary antenna module,

a separate pair of transmission paths coupled between each primary antenna module and a corresponding secondary antenna module, one of said pair of transmission paths being coupled between said radiating element oriented in one direction in said primary antenna module and said radiating element oriented in said one direction in said secondary antenna module, the other of said pair of transmission paths being coupled between said radiating element oriented in the other orthogonal direction in said primary antenna module and said radiating element oriented in said other direction in said secondary antenna module,

means for feeding electromagnetic energy to said primary array, whereby said energy received by the primary array is re-established and radiated by the secondary array independent of the polarization of said energy.

6. The combination as claimed in claim 5 wherein said primary antenna modules are arranged in a circular grid arrangement about a spherical section primary array and wherein said secondary antenna modules are arranged in a circular grid configuration about a planar secondary array.

7. The combination as claimed in claim 5 wherein said primary antenna modules are identically shaped and arranged as concentric rings to fill a spherical primary array and wherein said secondary antenna modules are identically shaped and arranged as concentric rings to fill the aperture of a planar secondary array.

8. The combination as claimed in claim 5 wherein said radiating elements are dipoles.

9. A transfer array antenna comprising:

a primary array including a plurality of primary antenna modules aperiodically arranged across the width of the aperture of the primary array so as to fill the aperture of the primary array, each of said primary antenna modules having only a single pair of orthogonally positioned radiating elements oriented in a given manner with respect to the sides of said primary antenna module.

a secondary array including a plurality of secondary antenna modules aperiodically arranged across the Width of the aperture of the secondary array so as to fill the aperture of the secondary array, each of said secondary antenna modules having a plurality of pairs of orthogonally placed radiating elements all oriented in the same given manner with respect to the sides of said secondary antenna module,

a separate pair of transmission paths coupled between each primary antenna module and a corresponding secondary antenna module, one transmission path of a pair of transmission paths being coupled between a radiating element oriented in one direction with remeans for feeding electromagnetic energy to said primary array, whereby said energy received by the primary array is radiated by the secondary array independent of the polarization of said energy.

References Cited UNITED STATES PATENTS 2,986,734 5/1961 Jones et a1. 343854 X 3,230,535 1/1966 Ferrante et al. 343754 3,245,081 4/1966 McFarland 343854 X 3,259,902 7/1966 Maleach 343854 X 3,354,461 11/1967 Kelleher 343-854 HERMAN KARL SAALBACH, Primary Examiner 25 T. T. VEZEAU, Assistant Examiner US. Cl. XJR. 

